1. Field of Invention
This invention describes the use of mechanical resonant longitudinal-torsional vibration to dissect biological tissue.
2. Description of Prior Art
The use of ultrasonic vibration to separate tissue was disclosed by Balamuth (U.S. Pat. No. 3,526,219) in 1970 who showed a variety of surgical instruments equipped with tips for different applications in the dissection of biological tissue. His devices provided motion either parallel also known as longitudinal, motion or perpendicular, known as parallel motion, to tissue surface. Kelman and Banko (U.S. Pat. No. 3,589,363) disclosed in 1971 apparatus and methods for dissecting and simultaneously aspirating tissue with a device that provided longitudinal tip contacting motion. Broadwin and Weiss (U.S. Pat. No. 4,136,700) later developed an aspirating ultrasonic tissue dissector that utilized transverse tip motion. Kelman (U.S. Pat. No. 4,504,264) and the Wuchinich (U.S. Pat. No. 5,176,677) patented ultrasonic dissectors that utilized, in addition to ultrasonic longitudinal tip motion, transverse tip ultrasonic motion with motor driven rotation to enhance tissue removal. Wuchinich (U.S. Pat. No. 4,750,902) also patented apparatus for the endoscopic dissection of tissue, combining the use of longitudinal ultrasonic vibration with aspiration, irrigation, telescopic vision and electro-cauterization.
Chief among the limitations of ultrasonic tissue dissection has been its feeble ability to separate collagenous tissue, bone and other connective or structurally supportive tissue. However, because ultrasonic vibration offers precise control and very little thermal and collateral damage, attempts have been repeatedly made to improve its performance on tissue otherwise resistant to its effect. Wuchinich shows one such invention (U.S. Pat. No. 5,176,677) for using transverse ultrasonic motion in combination with rotation to cut collagenous tissue such as cartilage and the meniscus.
All of the devices and methods that have been disclosed have not accomplished the object of rapid, precise removal of tissue normally resistant to ultrasonic dissection. Furthermore, although instruments that incorporate rotation of the tip, do offer improved performance on resistant tissue, because they require rotating seals and bearing they are complicated in construction, expensive to manufacture and fragile in use.
In 1969 Mitskevich described the development of, and experiments with, ultrasonic longitudinal-torsional resonators, known as L-T resonators. These ultrasonic devices are capable of transforming longitudinal motion into both longitudinal and torsional motion within one and same structure. Applications described by Mitskevich include welding and drilling. These resonators are also distinguished in converting imparted longitudinal motion from a transducer into both longitudinal and torsional motion at the tip of the L-T resonator. Such imparted longitudinal motion may be generated by any of the many common inexpensive electromechanical transducers for providing this motion by mechanical connection of such a transducer to the longitudinal torsional resonator. In 1981 Kleesatel (U.S. Pat. No. 4,281,987) connected a transducer providing longitudinal motion to an L-T resonator for the purpose of generating continuous rotary motion.
The resonators described by Mitskevich were made by creating an inhomogeneous cross section along the length of an otherwise uniform bar and then twisting the bar along its length. One way to create an inhomogeneous cross section to place grooves along the length of what was otherwise a round bar to create flutes. The resonator is then physically twisted about its axis, spiraling the grooves. The twisted bar is then connected to a transducer that produced longitudinal motion in response to application of an electrical current and voltage. The same structure can be obtained, and was evaluated by Mitskevich, by using a conventional twist drill or by machining the grooves into the bar. L-T resonators can also be made by twisting a bar containing a rectangular cross section about its axis to produce a spiral in exactly the way that drills were first made.
An L-T resonator containing a flat twisted section has the advantages of simplicity and economy in construction and can sustain greater torsional motion because the mass of the cross section remains uniformly distributed along its width. The mass of the cross section of the grooved twisted bar L-T resonator increases along its width or radius with the result that stress produced by torsional motion through the same angle is greater in this bar than in the flat twisted bar.
In 2000 Boukhny (U.S. Pat. No. 6,077,285) showed apparatus for providing both longitudinal and torsional ultrasonic tip for the purpose of enhancing tissue dissection. His device utilizes separate torsional and longitudinal transducers to provide this motion. As such, simultaneous operation of both transducers is described as providing both longitudinal and torsional motion of the working tip. However this system requires two electrical generators to supply the power, one each for each of the different transducers. Furthermore, all such devices, whether longitudinal, transverse or torsional must be fixed within an enclosure, such as a handpiece, preferably at points where there is no motion, known as motional nodes. However, because the wavelength of torsional and longitudinal vibration is, in general, substantially different, the node or nodes for longitudinal vibration and torsional motion will, in general, be located at different points on the transducer and other portions of other resonators attached to the transducers. Hence, in general, no true motionless point may be found with the result that either longitudinal or torsional motion will be communicated to the handpiece and thereby to the operator holding the handpiece. Although vibration isolators can be utilized to prevent the communication of such unintended motion, if they are truly isolating they invariably complicate construction of the device and, if simple, consume power in the form of heat generated by contact with a moving surface. Hence, Boukhn's device is both complicated to operate, needing two separate power sources, and difficult to construct.